Balancer device of engine and motorcycle

ABSTRACT

There is provided a balancer device of an engine, configured to reduce rotation vibrations of the engine. A crankshaft is provided with a primary drive gear. A countershaft is provided with a primary driven gear meshed with the primary drive gear. A plurality of balancer shafts are provided with balancer driven gears meshed with the primary drive gear.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2015-210356 filed onOct. 27, 2015, including specification, drawings and claims isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The disclosure relates to a balancer device of an engine and amotorcycle.

BACKGROUND

An engine of a motorcycle has been known which has a balancer device soas to reduce vibrations, which are to be generated in association withreciprocal movement of a piston and rotation of a crankshaft (forexample, refer to Patent Document 1 or Patent Document 2). In a balancerdevice disclosed in Patent Document 1 and Patent Document 2, a pair ofbalancer shafts having weights is disposed to be opposite to each otherwith sandwiching a crankshaft in a front-rear direction. One end of thecrankshaft is provided with drive gears for driving the balancer shafts,and the drive gears are meshed with driven gears provided for therespective balancer shafts. Thereby, the rotation of the crankshaft istransmitted to each of the balancer shafts, so that periodical rotationvibrations of the crankshaft are cancelled.

Patent Document 1: Japanese Patent Application Publication No.H02-113145A

Patent Document 2: Japanese Patent Application Publication No.2014-95405A

However, according to the engine disclosed in Patent Document 1 andPatent Document 2, while one end of the crankshaft is provided with thedrive gears for driving the balancer shafts, the other end of thecrankshaft is provided with a primary drive gear for driving acountershaft. In this way, since the drive gears for driving thebalancer shafts and the primary drive gear for driving the countershaftare separately provided, the engine is enlarged in a vehicle widthdirection. For example, when the crankshaft is provided with the drivegears corresponding to the number of the balancer shafts, the engine isfurther enlarged in the vehicle width direction by the drive gears,which causes a severer problem.

SUMMARY

It is therefore an object of the disclosure to provide an enginebalancer device and a motorcycle, in which balancer shafts can bedisposed without enlarging an engine.

According to an aspect of the embodiments of the present invention,there is provided a balancer device of an engine, configured to reducerotation vibrations of the engine, the balancer device comprising: acrankshaft provided with a primary drive gear; a countershaft providedwith a primary driven gear meshed with the primary drive gear; and aplurality of balancer shafts provided with balancer driven gears meshedwith the primary drive gear.

According to the above configuration, since it is possible to rotate thecountershaft and the plurality of balancer shafts by the existingprimary drive gear, it is not necessary to provide the crankshaft with agear for driving the balancer shaft. Therefore, as compared to aconfiguration where a gear for driving the balancer shaft is separatelyprovided from the primary drive gear, it is possible to shorten a lengthof the crankshaft, thereby reducing a width of the engine in aright-left direction. In this way, it is possible to dispose thebalancer shafts without enlarging the engine.

In the balancer device, the plurality of balancer shafts may comprise afirst balancer shaft disposed in front of the crankshaft and a secondbalancer shaft disposed below the crankshaft. According to the aboveconfiguration, since the second balancer shaft is disposed below thecrankshaft, it is possible to reduce a width in a front-rear directionof the engine, as compared to a configuration where the first balancershaft and the second balancer shaft are disposed in the front-reardirection.

In the balancer device, the primary drive gear may be provided at an endportion of the crankshaft, the second balancer shaft may be disposed atone side of the engine in a right-left direction, and an oil passageextending in a front-rear direction of the engine may be provided atanother side of the engine in the right-left direction. According to theabove configuration, since the second balancer shaft is disposed towardone side of the engine in the right-left direction and an empty space ofthe other side of the engine is provided with the oil passage, it ispossible to efficiently utilize a space in the engine and to form anoptimal oil passage. As a result, it is possible to make the enginecompact.

In the balancer device, the second balancer shaft may be disposed at anopposite side to a side stand configured to support a vehicle body withrespect to the right-left direction.

According to the above configuration, even when the side stand is usedand the engine is thus inclined toward the side stand-side, the secondbalancer shaft is located at a higher position than a liquid surface ofthe oil at the side stand-side. For this reason, it is possible toprevent the second balancer shaft from being submerged in the oil, sothat it is possible to reduce a mechanism loss upon start of the engine.

Also, the motorcycle of the disclosure may have the above-describedbalancer device of the engine.

According to the disclosure, the countershaft and the plurality ofbalancer shafts are rotated by the primary drive gear, so that it ispossible to dispose the balancer shafts without enlarging the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a side view depicting a schematic configuration of an engineof a motorcycle in accordance with an illustrative embodiment;

FIG. 2 is a front view of the engine shown in FIG. 1;

FIG. 3 is a side view depicting shaft arrangement in the engine inaccordance with the illustrative embodiment;

FIG. 4 is a front view depicting the shaft arrangement in the engine inaccordance with the illustrative embodiment;

FIG. 5 is a front view of a crank case in accordance with theillustrative embodiment;

FIG. 6 is a sectional view taken along a line A-A of the crank caseshown in FIG. 5;

FIG. 7 is a sectional view taken along a line B-B of the crank caseshown in FIG. 5;

FIG. 8 is a side view depicting a state where a clutch cover is detachedfrom the engine in accordance with the illustrative embodiment;

FIG. 9 is a bottom view depicting a state where an oil pan is detachedfrom the engine in accordance with the illustrative embodiment; and

FIG. 10 is a front view of the engine when a side stand is used for amotorcycle in accordance with an illustrative embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, an illustrative embodiment of the disclosure will bedescribed in detail with reference to the accompanying drawings.Meanwhile, in the below, an example where a balancer device of an engineof the disclosure is applied to a motorcycle will be described. However,the disclosure is not limited thereto. For example, the balancer deviceof the engine of the disclosure may also be applied to a motorcycle ofother type, a three-wheeled motor vehicle of a buggy type, afour-wheeled motor vehicle, or the like. Also, regarding directions, avehicle front side is denoted with an arrow FR, a vehicle rear side isdenoted with an arrow RE, a vehicle left side is denoted with an arrowL, and a vehicle right side is denoted with an arrow R, respectively.Also, in the respective drawings, some configurations are omitted forconvenience of explanations.

A schematic configuration of an engine of a motorcycle in accordancewith an illustrative embodiment is described with reference to FIGS. 1and 2. FIG. 1 is a side view depicting a schematic configuration of anengine of a motorcycle in accordance with an illustrative embodiment.FIG. 2 is a front view of the engine shown in FIG. 1.

As shown in FIGS. 1 and 2, an engine 1 is a two-cylinder four-cycleengine and has constitutional components such as pistons 22 (refer toFIG. 3) and the like accommodated in a cylinder assembly 12 configuredby a cylinder block 10 and a cylinder head 11, and a cylinder head cover13 is attached to an upper end of the cylinder assembly 12 (cylinderhead 11). A crank case 2 configured to accommodate therein a crankshaft20 (refer to FIG. 3) is attached to a rear-lower side of the cylinderassembly 12.

The crank case 2 is configured to be vertically separable and has anupper case 3 and a lower case 4. When the upper case 3 and the lowercase 4 are combined, a space for accommodating a variety of shafts inthe crank case 2 is formed. A front-upper part of the upper case 3opens, and the cylinder block 10 is attached to the upper case 3 so asto block the opening. The lower case 4 opens downward, and an oil pan 5is attached to the lower case 4 so as to block the opening.

Also, an oil cooler 14 configured to cool oil in the engine 1 and an oilfilter 15 (which is not shown in FIG. 1) configured to filter uncleanoil are attached to a front part of the lower case 4. As shown in FIG.2, the oil cooler 14 is provided at a right side of the front part ofthe lower case 4 and the oil filter 15 is provided at a left side.

Both left and rights sides of the crank case 2 are formed with openings,respectively. A magneto cover 16 (which is not shown in FIG. 1)configured to cover a magneto (not shown) is attached to the leftopening, and a clutch cover 17 configured to cover a clutch (not shown)is attached to the right opening. A water pump 18 configured to supplycooling water into the engine 1 is provided in front of the clutch cover17. Also, although not shown, a side stand 19 (refer to FIG. 10)configured to support a vehicle body (engine 1) is provided at aleft-lower side of the crank case 2.

Subsequently, shaft arrangement in the crank case and a balancer devicein accordance with the illustrative embodiment are described withreference to FIGS. 3 and 4. FIG. 3 is a side view depicting the shaftarrangement in the engine in accordance with the illustrativeembodiment. FIG. 4 is a front view depicting the shaft arrangement inthe engine in accordance with the illustrative embodiment. In FIGS. 3and 4, the crank case is not shown and only the shaft arrangement isshown for convenience of explanations.

As shown in FIGS. 3 and 4, not only the crankshaft 20 but also a varietyof shafts for transmitting a driving force of the engine 1 (refer toFIG. 1) are accommodated in the crank case 2 (refer to FIG. 1). In thebelow, arrangement positions of the diverse shafts are described on thebasis of a position of the crankshaft 20. The crankshaft 20 isaccommodated at the slight front of a center of the crank case 2 (referto FIG. 6 or 7). Two pistons 22 are axially side by side attached to thecrankshaft 20 via connecting rods 21. Meanwhile, a crank phase of thecrankshaft 20 in accordance with the illustrative embodiment is set to270°. Also, a right end portion of the crankshaft 20 is provided with aprimary drive gear 20 a for driving the diverse shafts in the engine 1so that the primary drive gear can integrally rotate.

A countershaft 23 is provided at an oblique upper side of the rear ofthe crankshaft 20. A right end of the countershaft 23 is provided with aclutch (not shown), and a primary driven gear 23 a is provided close tothe clutch at an inner side of the clutch in a vehicle width direction.

The primary driven gear 23 a is attached to the countershaft 23 so thatit can integrally rotate, and is meshed with the primary drive gear 20a. Also, the countershaft 23 is provided with a variety of gears fortransmission at the left of the primary driven gear 23 a.

A drive shaft 24 is provided at an oblique lower side of the rear of thecountershaft 23. The drive shaft 24 is provided with a variety of gearsfor transmission. Also, a plurality of (two, in the illustrativeembodiment) balancer shafts 25 configuring a part of the balancer deviceis provided around the crankshaft 20.

The balancer shafts 25 include a first balancer shaft 26 disposed at thefront of the crankshaft 20 and a second balancer shaft 27 disposed below(just below) the crankshaft 20. The first balancer shaft 26 and thesecond balancer shaft 27 are disposed so that an angle between a lineconnecting the first balancer shaft 26 and the crankshaft 20 and a lineconnecting the second balancer shaft 27 and the crankshaft 20 issubstantially a right angle.

The first balancer shaft 26 and the second balancer shaft 27 extendalong an axial direction of the crankshaft 20. A first balancer drivengear 26 a configured to mesh with the primary drive gear 20 a isprovided at a right end portion of the first balancer shaft 26 so as tobe integrally rotatable. The first balancer shaft 26 is provided withtwo balancer weights 26 b aligned side by side in the axial direction incorrespondence to the positions of the two pistons 22.

A second balancer driven gear 27 a configured to mesh with the primarydrive gear 20 a is provided at a right end portion of the secondbalancer shaft 27 so as to be integrally rotatable. The second balancershaft 27 is provided with a balancer weight 27 b at a positioncorresponding to the right piston 22. The second balancer shaft 27 isdisposed at one side (right side) of the engine 1, i.e., the same sideas the clutch.

Also, side surfaces of the first balancer driven gear 26 a and thesecond balancer driven gear 27 a are provided with reference marks 26 c,27 c, which are references when phase adjusting the two balancer shafts25 relative to the crankshaft 20. Likewise, a side surface of theprimary drive gear 20 a attached to the crankshaft 20 is also providedwith two reference marks (not shown).

When mounting the two balancer shafts 25 to the crank case 2, thereference marks 26 c, 27 c of the first balancer driven gear 26 a andthe second balancer driven gear 27 a are matched with the respectivereference marks of the crankshaft 20, so that it is possible to adjustthe two balancer shafts 25 to a predetermined phase with respect to thecrankshaft 20.

In the engine 1 configured as described above, rotation of thecrankshaft 20 is transmitted to the countershaft 23 via the primarydrive gear 20 a and the primary driven gear 23 a. The rotation of thecountershaft 23 is transmitted to the drive shaft 24 with apredetermined change gear ratio by combinations of the diverse gears.The rotation of the drive shaft 24 is transmitted to a rear wheel (notshown) via a transmission mechanism (not shown).

Also, the rotation of the crankshaft 20 is transmitted to the twobalancer shafts 25 configuring the balancer device, too. Specifically,the rotation of the crankshaft 20 is transmitted to the first balancershaft 26 via the primary drive gear 20 a and the first balancer drivengear 26 a, and the rotation of the crankshaft 20 is transmitted to thesecond balancer shaft 27 via the primary drive gear 20 a and the secondbalancer driven gear 27 a.

The vibrations of the engine 1 generated in association with therotation of the crankshaft 20 are cancelled by the rotations of thefirst balancer shaft 26 and the second balancer shaft 27. The vibrationsof the engine 1 are reduced in this way, so that it is possible tosuppress an influence of the vibrations or noises on a passenger.

In the meantime, the balancer device of the motorcycle has been mainlyconfigured by one balancer shaft. However, since the vibrations of theengine increase in a vehicle of large engine displacement or a vehiclerequired to have a supercharger, it is not possible to achieve thesufficient effect of attenuating the vibrations by one balancer shaft.Regarding this, a balancer device having two or more balancer shafts hasbeen suggested. However, the balancer shafts cause an increase in weightof the engine and enlarge the engine due to the shaft arrangement in theengine.

For example, when the two balancer shafts are vertically disposed, theengine is enlarged in a height direction. In this case, the lowerbalancer shaft is submerged into the oil in the oil pan, so that amechanism loss is generated. Therefore, it is necessary to dispose thebalancer shaft at a predetermined height with respect to an oil surfaceof the oil pan. Also, when the two balancer shafts are disposed in afront-rear direction, the engine is enlarged in the front-reardirection. Particularly, in recent motorcycles, a wheelbase of a vehicleis reduced to secure a comfortable riding feeling.

Also, as described above, the drive gear for driving the balancer shaftand the primary drive gear for driving the countershaft are generallyseparately provided for the crankshaft. For this reason, it is necessaryto further lengthen the crankshaft by a magnitude corresponding to thedrive gear for driving the balancer shaft, so that the engine isenlarged in the vehicle width direction. Like this, there are manyrestraints on the arrangement of the diverse components in the engine,and a new problem may be caused due to the arrangement.

Therefore, in the illustrative embodiment, the shaft arrangement in theengine 1 is changed to drive the three shafts of the countershaft 23 andthe two balancer shafts 25 (the first balancer shaft 26 and the secondbalancer shaft 27) with one primary drive gear 20 a. Thereby, it ispossible to drive the two balancer shafts 25 only with the existingprimary drive gear 20 a and it is not necessary to separately providethe gear for driving the balancer shaft. As a result, it is possible toreduce the width of the engine 1 in the right-left direction withoutextending the crankshaft 20. Further, since it is possible to configurea gear, which is to be provided for the crankshaft 20, only by the oneprimary drive gear 20 a, it is possible to save the processing cost ofthe crankshaft 20, thereby achieving the cost down.

Also, the first balancer shaft 26 is provided at the front of thecrankshaft 20 and the second balancer shaft 27 is provided below thecrankshaft 20, so that it is possible to dispose the two balancer shafts25 in the engine 1 without increasing the widths in the upper-lowerdirection and the front-rear direction of the engine 1. By theseconfigurations, it is possible to make the engine compact as a whole.

Also, as described above, the three shafts are driven by the one primarydrive gear 20 a and the respective gears (the primary driven gear 23 a,the first balancer driven gear 26 a and the second balancer driven gear27 a) are intensively disposed at the right side. Thereby, it ispossible to check the reference marks 26 c, 27 c of the first balancerdriven gear 26 a and the second balancer driven gear 27 a at the sametime, so that it is possible to improve the mounting ability of the twobalancer shafts 25.

Also, in the illustrative embodiment, since the first balancer shaft 26and the water pump 18 (refer to FIG. 1) are coaxially provided, it ispossible to drive the water pump 18 by using the rotation of the firstbalancer shaft 26 as a driving source. Therefore, it is not necessary toprovide a dedicated gear for the water pump 18 and it is possible tosimplify the configuration.

Subsequently, a positional relation between the diverse shafts in theengine and the crank case and the internal configuration of the crankcase are described with reference to FIGS. 5 to 8. FIG. 5 is a frontview of the crank case in accordance with the illustrative embodiment.FIG. 6 is a sectional view taken along a line A-A of the crank caseshown in FIG. 5. FIG. 7 is a sectional view taken along a line B-B ofthe crank case shown in FIG. 5. In FIG. 7, the oil pan is not shown forconvenience of explanations. FIG. 8 is a side view depicting a statewhere the clutch cover and the oil pan are detached from the engine inaccordance with the illustrative embodiment.

As shown in FIGS. 5 and 6, in the illustrative embodiment, thecrankshaft 20 and the first balancer shaft 26 are disposed on matingsurfaces of the upper case 3 and the lower case 4. More specifically,the mating surfaces of the upper case 3 and the lower case 4 are formedwith two bearings in the front-rear direction. The first balancer shaft26 is disposed in the front bearing, and the crankshaft 20 is disposedin the rear bearing. Also, the second balancer shaft 27 is supported bythe lower case 4 and the balancer housing 6 configured to accommodatetherein the second balancer shaft 27. Mating surfaces of the lower case4 and the balancer housing 6 are formed with a bearing in which thesecond balancer shaft 27 is disposed.

The lower case 4 and the balancer housing 6 are respectively formed witha plurality of through-holes 40, 60 (only two through-holes are shown,respectively, in FIG. 6) in which fastening bolts 7 are to be inserted.The plurality of through-holes 40, 60 is formed at positions betweenwhich the crankshaft 20 or the second balancer shaft 27 is sandwiched inthe front-rear direction. Also, the upper case 3 is formed with screwholes (not shown) at positions corresponding to the plurality ofthrough-holes 40, 60. The fastening bolts 7 are inserted into thethrough-holes 40, 60 from the lower of the balancer housing 6 and arethen screwed into the upper case 3, so that the upper case 3, the lowercase 4 and the balancer housing 6 are integrally fixed.

In this way, the crankshaft 20, the first balancer shaft 26 and thesecond balancer shaft 27 are arranged on the mating surfaces of thecrank case 2 and the balancer housing 6, so that it is possible toattach the corresponding shafts just by sandwiching the same with theupper case 3, the lower case 4 and the balancer housing 6.

Particularly, the first balancer shaft 26 can be mounted to the crankcase 2 with the first balancer driven gear 26 a and the balancer weight26 b being assembled in advance. The second balancer shaft 27 can alsobe mounted to the crank case 2 with the second balancer driven gear 27 aand the balancer weight 27 b being assembled in advance. As a result,the mounting ability of the engine 1 is improved.

Also, since the balancer housing 6 is formed to cover the lower side ofthe second balancer shaft 27, it is possible to support the secondbalancer shaft 27 simply by covering the crank case 2 (lower case 4)with the balancer housing 6. Thereby, the mounting ability of the engine1 is improved. Also, for a vehicle where the second balancer shaft 27 isnot used, for example, it is possible to easily change a design byomitting the balancer housing 6 to shorten a length of the fasteningbolt 7. For this reason, it is possible to save the design man-hour,too.

Further, since the upper case 3, the lower case 4 and the balancerhousing 6 are together fastened by the fastening bolts 7, it is possibleto reduce the number of the fastening bolts 7 to be used, as compared toa configuration where the bolt fastening is performed for each of thecrankshaft 20 and the second balancer shaft 27. Thereby, it is possibleto reduce the mounting man-hour and an operator's burden on the boltfastening. Also, even when combining the respective bearings (bearingsof the crankshaft and the two balancer shafts 25), it is possible toreduce the number of times of the bolt fastening, so that it is possibleto save the processing man-hour and to improve the operation efficiency.

Herein, an oil passage in the crank case 2 is described. As shown inFIG. 6, the lower case 4 is provided with a main oil gallery 41, whichconfigures a part of the oil passage in the engine 1, below the firstbalancer shaft 26 and in front of the second balancer shaft 27. The mainoil gallery 41 extends in the right-left direction.

Also, the lower case 4 is formed with oil passages 42, 43 for supplyingthe oil from the main oil gallery 41 to the crankshaft 20 and the firstbalancer shaft 26 and an oil passage 44 for supplying the oil from thecrankshaft 20 to the second balancer shaft 27. Further, the oil passage44 is formed with an oil passage 45 for supplying the oil to the driveshaft 24 (refer to FIG. 3). The oil passages 42, 45 are formed toobliquely penetrate the plurality of through-holes 40. Thereby, it ispossible to utilize the through-hole 40 for the fastening bolt 7 as apart of the oil passage.

Meanwhile, the upper case 3 is provided with a sub-oil gallery 30 abovethe first balancer shaft 26. The sub-oil gallery 30 extends in theright-left direction. Also, the upper case 3 is formed with an oilpassage 31 for supplying the oil from the main oil gallery 41 to thesub-oil gallery 30 through the first balancer shaft 26.

In the illustrative embodiment, the above-described shaft arrangement isadopted and the main oil gallery 41 and the sub-oil gallery 30 areprovided in an empty space near the two balancer shafts 25. Thereby, itis possible to form the oil passage to each shaft (bearing) as a linearthrough-hole. For this reason, it is possible to form the oil passage bysimple hole processing, so that it is possible to save the processingman-hour.

Also, since the crankshaft 20 and the second balancer shaft 27 aredisposed adjacent to each other in the lower case 4, it is possible toeasily form the oil passage between the crankshaft 20 and the secondbalancer shaft 27 by the hole processing. Therefore, it is possible tosave a weight of the crank case 2, as compared to a configuration wherean independent oil passage is separately formed using an unnecessarythickness of the crank case 2.

Also, as shown in FIGS. 7 and 8, in the engine 1, the oil is reserved inthe oil pan 5. The oil is pumped by an oil pump (not shown) and is thensupplied to each part in the engine 1 through the main oil gallery 41,the sub-oil gallery 30 and the like. In the illustrative embodiment, aliquid surface of the oil is positioned at a height at which the secondbalancer driven gear 27 a and the balancer weight 27 b of the secondbalancer shaft 27 are not submerged. For this reason, it is possible toprevent the oil from becoming a rotation resistance (mechanism loss) ofthe second balancer shaft 27. Also, it is possible to prevent the rotarybodies (the second balancer driven gear 27 a and the balancer weight 27b) from stirring the oil to introduce air bubbles into the oil.

Also, as described above, the liquid surface height of the oil is set tothe height at which the rotary bodies are not submerged. Thereby, eventhough the oil surface move in waves when the vehicle body is bankedduring the cornering, for example, it is possible to prevent the oilfrom directly colliding with the rotary bodies.

Further, the second balancer shaft 27 is provided just below thecrankshaft 20, so that it is possible to interrupt a descending aircurrent, which is to be generated when the pistons 22 (refer to FIG. 3)moves downward, by the balancer housing 6 (refer to FIG. 6). That is, itis possible to achieve a windshield effect by the balancer housing 6becoming a wall. For this reason, the liquid surface of the oil reservedin the oil pan 5 does not undulate by the descending air current.Therefore, it is possible to prevent a situation where the air bubblesare introduced into the oil and the lubrication performance is thuslowered.

Also, as shown in FIG. 8, the right side of the crank case 2 is formedwith an opening 29 for accommodating the clutch (not shown) by anannular peripheral wall part 28. The peripheral wall part 28 has a shapeconforming to a profile of the clutch cover 17 (refer to FIG. 1 or 2).Also, an end surface (side surface) of the peripheral wall part 28configures a mating surface 28 a with the clutch cover 17. The clutchcover 17 is attached along the mating surface 28 a, so that the opening29 is blocked.

At a state where the clutch cover 17 is detached, parts of thecrankshaft 20 and the second balancer shaft 27 are positioned in theopening 29, as seen from a side of the engine 1. More specifically,parts of the primary drive gear 20 a and the second balancer driven gear27 a and the bearings of the crankshaft 20 and the second balancer shaft27 are disposed in a space surrounded by the annular peripheral wallpart 28.

In this way, parts of the crankshaft 20 and the second balancer shaft 27are exposed to an outside, so that it is possible to easily recognizethe reference mark 27 c for phase adjustment. That is, it is possible toutilize the opening 29 of the crank case 2, which occupies most of theside surface of the engine 1, as a viewing window for phase adjustmentof the second balancer shaft 27. Thereby, it is possible to phase-adjustthe second balancer shaft 27 relative to the crankshaft 20 withoutproviding a dedicated viewing window.

Also, it is not necessary to perform hole processing for forming adedicated viewing window and to provide a blind plug for blocking thehole, so that it is possible to simplify the configuration of the crankcase 2. Further, the blind plug is not required, so that an outwardappearance of the engine 1 is not influenced.

Also, the bearings of the crankshaft 20 and the second balancer shaft 27are exposed from the opening 29 of the crank case 2, so that it ispossible to secure a wide space when processing the bearings. That is,since it is possible to secure a wide area for supporting a processingtool, it is possible to stably support the processing tool to the matingsurface 28 a. Therefore, it is possible to suppress shaking upon theprocessing of the bearings (holes), so that it is possible to improveprocessing precision.

Also, since only parts (bearings) of the crankshaft 20 and the secondbalancer shaft 27 are exposed, instead of entirely exposing the same, itis possible to form the opening 29 of the crank case 2 to a minimalsize. Therefore, it is possible to increase the rigidity of the crankcase 2, as compared to a configuration where the respective shafts areentirely exposed.

Subsequently, a positional relation between the shaft arrangement andthe oil passage in the crank case is described with reference to FIG. 9.FIG. 9 is a bottom view depicting a state where the oil pan is detachedfrom the engine in accordance with the illustrative embodiment.

As shown in FIG. 9, the second balancer shaft 27 is disposed at theright side of the engine 1 (lower case 4). Also, a space of an oppositeside (left side) of the second balancer shaft 27 is provided with acylindrical oil passage 46 extending in the front-rear direction. Theoil passage 46 configures a path for supplying the oil from the oil pump(not shown) to the oil filter 15. In this way, the primary drive gear 20a (not shown in FIG. 9) and the second balancer shaft 27 are disposed atone side (right side) of the engine 1 in the right-left direction andthe left empty space of the engine 1 is provided with the oil passage46, so that it is possible to efficiently utilize the space in theengine 1. As a result, it is possible to form an optimal oil passagewithout enlarging the engine 1, so that it is possible to make theengine 1 compact.

Subsequently, the oil surface in the engine when a side stand is used isdescribed with reference to FIG. 10. FIG. 10 is a front view of theengine when a side stand is used for a motorcycle in accordance with anillustrative embodiment.

As shown in FIG. 10, a side stand 19 configured to support the vehiclebody (engine 1) is provided at the left of the engine 1 and below thecrank case 2 (lower case 4) (at the left of the oil pan 5). At a statewhere the vehicle body is supported by the side stand 19, the vehicle isinclined toward the side stand-side (left side), so that the engine 1 isinclined.

As described above with reference to FIG. 3, the second balancer shaft27 is disposed at the right side of the engine 1. That is, the secondbalancer shaft 27 is disposed at an opposite side to the side stand 19.Therefore, even when the side stand 19 is used and the engine 1 is thusinclined toward the side stand 19-side, the second balancer shaft 27 islocated at a higher position than the liquid surface of the oil at theside stand 19-side. For this reason, it is possible to prevent thesecond balancer shaft 27 from being submerged in the oil, so that it ispossible to reduce the mechanism loss upon the start of the engine.

Also, it is possible to prevent the rotary bodies such as the secondbalancer driven gear 27 a and the balancer weight 27 b provided for thesecond balancer shaft 27 from stirring the oil to introduce the airbubbles into the oil.

As described above, according to the illustrative embodiment, since itis possible to rotate the countershaft 23 and the two balancer shafts 25(the first balancer shaft 26 and the second balancer shaft 27) by theexisting primary drive gear 20 a, it is not necessary to provide thecrankshaft 20 with a gear for driving the balancer shaft. Therefore, ascompared to a configuration where a gear for driving the balancer shaftis separately provided from the primary drive gear 20 a, it is possibleto shorten a length of the crankshaft 20, thereby reducing the width ofthe engine 1 in the right-left direction. In this way, it is possible todispose the two balancer shafts 25 without enlarging the engine 1.

In the meantime, the disclosure is not limited to the illustrativeembodiment and can be diversely changed and implemented. In theillustrative embodiment, the sizes, shapes and the like shown in theaccompanying drawings are not limited thereto and can be appropriatelychanged within a scope of achieving the effects of the disclosure. Inaddition, the illustrative embodiment can be appropriately changedwithout departing from the object of the disclosure.

For example, in the above illustrative embodiment, the balancer devicehaving the two balancer shafts 25 has been described. However, thedisclosure is not limited thereto. For example, the balancer device mayhave one balancer shaft or three or more balancer shafts.

Also, in the above illustrative embodiment, the first balancer shaft 26is provided with the two balancer weights 26 b. However, the disclosureis not limited thereto. For example, only one balancer weight 26 b maybe provided for the first balancer shaft 26. In this case, the balancerweight 26 b is preferably provided in front of the left piston 22.

Also, in the above illustrative embodiment, the first balancer shaft 26and the balancer weight 26 b are configured as separate components.However, the disclosure is not limited thereto. For example, the firstbalancer shaft 26 and the balancer weight 26 b may be integrallyconfigured. The second balancer shaft 27 and the balancer weight 27 bmay also be integrally configured without being limited to theconfiguration where they are configured as separate components.

As described above, the disclosure has the effect of disposing thebalancer shafts without enlarging the engine, and is particularly usefulfor the balancer device of the engine and the motorcycle.

What is claimed is:
 1. A balancer device of an engine, configured to reduce rotation vibrations of the engine, the balancer device comprising: a crankshaft provided with a primary drive gear; a countershaft provided with a primary driven gear meshed with the primary drive gear; and a plurality of balancer shafts provided with balancer driven gears meshed with the primary drive gear.
 2. The balancer device according to claim 1, wherein the plurality of balancer shafts comprises a first balancer shaft disposed in front of the crankshaft and a second balancer shaft disposed below the crankshaft.
 3. The balancer device according to claim 2, wherein the primary drive gear is provided at an end portion of the crankshaft, wherein the second balancer shaft is disposed at one side of the engine in a right-left direction, and wherein an oil passage extending in a front-rear direction of the engine is provided at another side of the engine in the right-left direction.
 4. The balancer device according to claim 2, wherein the second balancer shaft is disposed at an opposite side to a side stand configured to support a vehicle body with respect to the right-left direction.
 5. A motorcycle comprising the balancer device according to claim
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